The present invention relates to a process for producing an electrodeposited copper foil, an electrodeposited copper foil obtained by such a process, a copper-clad laminate for which the electrodeposited copper foil is used and a printed wiring board. More particularly, the present invention relates to a producing process of an electrodeposited copper foil in which lead (Pb) ions contained as impurities in the electrolyte are removed to thereby prevent codeposition of fine particles (fine powder) of Pb and/or Pb compounds (mainly lead oxides); and an electrodeposited copper foil produced by the process, which is substantially free from fine particles of Pb and/or Pb compounds. The present invention further relates to a copper-clad laminate produced using the electrodeposited copper foil, which comprises a substrate having at least one side thereof laminated with the electrodeposited copper foil; and a printed wiring board produced using the electrodeposited copper foil.
In the continuous production of an electrodeposited copper foil, it is common practice to arrange a cylindrical drum as a cathode and, opposite thereto, an insoluble anode in an electrolyte in which a copper material such as copper sulfate is dissolved and to carry out electrolysis so that copper is electrodeposited on the surface of the cylindrical drum.
In recent years, electronic equipment is being miniaturized and densified, and accordingly circuit widths and circuit spacings of printed wiring boards used in such electronic equipment are being reduced. The use of a thin electrodeposited copper foil with low surface roughness (profile) is desired in accordance with the above reduction of circuit widths and circuit spacings.
Though the surface profile of electrodeposited copper foil is apt to be lowered with reduction in the thickness of the electrodeposited copper foil, there are various methods for further lowering the surface profile. For example, the surface profile of electrodeposited copper foils can be controlled by adjusting the Cl ion (chloride ion) concentration of the electrolyte. In particular, the electrodeposited copper foil with low surface profile that enables forming a fine-pitch wiring pattern can be produced by adjusting the Cl ion concentration of the electrolyte so as to be a given range.
However, when lead (Pb) ions are contained as impurities in the electrolyte in the production of electrodeposited copper foils with the use of an electrolyte of low Cl ion concentration, co-deposition of dendrite-like fine particles of Pb with copper may be experienced. The diameter of the thus co-deposited fine particles of Pb is generally in the range of 1 to 50 xcexcm, frequently 5 to 30 xcexcm. Fine particles of Pb are often deposited in the vicinity of the surface of electrodeposited copper foil. In such electrodeposition, Pb compounds such as lead oxides may be co-deposited as fine particles, in addition to the fine particles of Pb.
These co-deposited fine particles of Pb, etc., although few problems are caused thereby when the circuit widths are large as before, tend to cause such problems that copper foil circuits are discontinuous and circuits are broken since the thickness of the copper foil is reduced in accordance with the aforementioned reduction of circuit widths. Further, since the fine particles of Pb can not be removed from the copper foil by the conventional etching technique, the fine particles of Pb may cause short circuit of printed wiring board using the copper foil.
Generally, the surface of the thus electrodeposited copper foil is provided with various treatments in order to impart required properties to the resultant circuit pattern or printed wiring board. For example, the surface of the electrodeposited copper foil is roughened at a limiting current density or over and subjected to various platings such as zinc plating, tin plating and nickel plating, and the surface of the thus formed plate layer is subjected to chromate treatment and silane coupling agent treatments.
When these various treatments are performed on the copper foil surface, it is extremely difficult to detect fine particles of Pb co-deposited into the copper foil. Therefore, in the industrial process for producing wiring boards, it is practically infeasible to identify portions of co-deposition of Pb fine particles in the produced electrodeposited copper foil and to arrange the process so that such portions are substantially not utilized.
In this connection, it is common practice to use an electrode (anode) of a lead alloy in the above production of electrodeposited copper foils using a cylindrical drum. When a lead alloy is used as an anode, leaching of lead into the electrolyte is likely to occur. It is known that, when lead is leached to thereby cause the concentration of Pb ions in the electrolyte to increase to a given level or over, the Pb ions are co-deposited into the copper foil (reference is made to, for example, Japanese Patent Application Publication (unexamined) Nos. Hei 6-146051 and Hei 6-146052).
These publications disclose the effect that the addition of strontium carbonate is effective in the removal of lead ions from the electrolyte containing lead ions as impurities. Specifically, it is described that, when the concentration of lead ions is relatively high as, for example, in the case where an electrode containing lead is used as an anode, the lead ions contained in the electrolyte can be eliminated by adding strontium carbonate, and that the thus formed lead/strontium composite can be removed with relatively high efficiency by filtering the electrolyte.
However, for accomplishing the co-deposition of the lead/strontium composite, it is requisite that the concentration of lead ions in the electrolyte be relatively high. Therefore, in the case where no lead containing electrode is employed, it is extremely difficult to eliminate lead ions having been mixed in an extremely small amount into the electrolyte in the production of the electrolyte by the above addition of strontium electrolyte and remove the precipitate by filtration.
As apparent from the above, in the process for producing an electrodeposited copper foil through deposition of copper on a cylindrical drum in an electrolyte containing an extremely small amount of lead ions as conducted in the present invention, no technology has been established for effectively preventing a small amount of fine particles of lead from being contained in the electrodeposited copper foil by relatively simple operation such as filtration.
The present invention provides a process in which co-deposition of fine particles of lead can effectively be prevented in the deposition of a copper foil from an electrolyte containing copper sulfate dissolved therein with the use of a cylindrical drum as a cathode.
The present invention also provides an electrodeposited copper foil substantially free from any fine particles of Pb and/or Pb compounds, which electrodeposited copper foil is obtained by electrodeposition from an electrolyte containing copper sulfate dissolved therein with the use of a cylindrical drum as a cathode.
The present invention further provides a copper-clad laminate comprising an insulating substrate comprising the above electrodeposited copper foil substantially free from any fine particles of Pb and/or Pb compounds, which copper foil is laminated on the surface of the substrate, and to provide a printed wiring board furnished with a desirable wiring pattern, which printed wiring board is produced from the electrodeposited copper foil substantially free from any fine particles of Pb and/or Pb compounds.
In one aspect of the present invention, there is provided a process for producing an electrodeposited copper foil, said copper foil being electrodeposited from an electrolyte containing copper sulfate dissolved therein, in which said electrolyte contains a small amount of lead (Pb) ions, which comprises adding a salt of a metal of Group IIA of the periodic table to the electrolyte in an amount of 10 to 150 mol per mol of lead (Pb) ions contained in the electrolyte so that the lead (Pb) ions contained in the electrolyte is precipitated as an insoluble composite substance with the metal of Group IIA of the periodic table, removing insoluble composite substance from the electrolyte, and forming an electrodeposited copper foil from the electrolyte of which the lead (Pb) ions have been removed therefrom.
The electrodeposited copper foil of the present invention is produced by the above process and substantially free from any fine particles of Pb and/or Pb compounds.
Thus, in another aspect of the present invention, there is provided an electrodeposited copper foil produced by a process for producing an electrodeposited copper foil, said copper foil being electrodeposited from an electrolyte containing copper sulfate dissolved therein, in which said electrolyte contains a small amount of lead (Pb) ions, which comprises adding a salt of a metal of Group IIA of the periodic table to the electrolyte in an amount of 10 to 150 mol per mol of lead (Pb) ions contained in the electrolyte so that the lead (Pb) ions contained in the electrolyte is deposited as an insoluble composite substance with the metal of Group IIA of the periodic table, removing insoluble composite substance from the electrolyte, and forming an electrodeposited copper foil from the electrolyte of which the lead (Pb) ions have been removed therefrom.
The copper-clad laminate of the present invention comprises an insulating substrate and the above electrodeposited copper foil is substantially free from any fine particles of Pb and/or Pb compound (mainly lead oxides), which copper foil is laminated on at least one surface of the substrate.
Accordingly, in a further aspect of the present invention, there is provided a copper-clad laminate comprising an insulating substrate and an electrodeposited copper foil laminated on at least one surface thereof, which is produced by a process for producing electrodeposited copper foil, said copper foil is electrodeposited from an electrolyte containing copper sulfate dissolved therein, in which said electrolyte contains a small amount of lead (Pb) ions, which comprises adding a salt of a metal of Group IIA of the periodic table to the electrolyte in an amount of 10 to 150 mol per mol of lead (Pb) ions contained in the electrolyte so that the lead (Pb) ions contained in the electrolyte is eliminated as an insoluble composite substance with the metal of Group IIA of the periodic table, removing insoluble composite substance from the electrolyte, and forming an electrodeposited copper foil from the electrolyte of which the lead (Pb) ions have been removed therefrom.
Still further, the printed wiring board of the present invention is produced by treating the electrodeposited copper foil of the above copper-clad laminate comprising an insulating substrate comprising the electrodeposited copper foil substantially free from any fine particles of Pb and/or Pb compound (mainly lead oxides), which copper foil is laminated on at least one surface of the substrate, so as to form a desirable wiring pattern.
Thus, in a still further aspect of the present invention, there is provided a printed wiring board furnished with a desirable wiring pattern, produced by etching at its electrodeposited copper foil on a copper-clad laminate comprising an insulating substrate and an electrodeposited copper foil laminated on at least one surface thereof, which is produced by a process for producing an electrodeposited copper foil, said copper foil being electrodeposited from an electrolyte containing copper sulfate is dissolved therein, in which said electrolyte contains a small amount of lead (Pb) ions, which comprises adding a salt of a metal of Group IIA of the periodic table to the electrolyte in an amount of 10 to 150 mols per mol of lead (Pb) ions contained in the electrolyte so that the lead (Pb) ions contained in the electrolyte are precipitated as an insoluble composite substance with the metal of Group ILA of the periodic table, removing insoluble composite substance from the electrolyte, and forming an electrodeposited copper foil in the electrolyte of which the lead (Pb) ions have been removed therefrom.
The present invention has been completed on the basis of such findings that, when a small amount of lead (Pb) ions is contained in the electrolyte, the addition of a salt of a metal of Group IIA of the periodic table in a specified amount relative to the amount of lead (Pb) ions contained in the electrolyte causes the small amount of lead (Pb) ions contained in the electrolyte to precipitate with the added metal of Group IIA of the periodic table and that the precipitate can be removed by a customary separating operation such as filtration.
It is preferred that the electrolyte used in the process for producing electrodeposited copper foil of the invention have a chloride ion (Clxe2x88x92) concentration adjusted in the range of 0.1 to 5.0 mg/l, in order to make the rough surface of the copper foil have even surface roughness (profile).